A compact disk (CD) is an example of a data recording disk on which a digital signal is recorded. A CD is a small digital audio disk having a diameter of about 12 cm. Recently, another type of disk, referred to as a composite disk or CDV, has been placed on the market which has the same dimensions as a CD and on which an FM modulated video signal and a PCM (Pulse Code Modulation) signal are recorded in a multiplexed form in addition to an another signal recorded solely in PCM form.
In such a composite disk, as shown in FIG. 1, the two types of data are recorded in two respective distinct regions of the disk. In a first region 1a (hereinafter referred to as a CD region) in an inner circumferential portion of the disk, a PCM audio data signal is recorded, and in a second region 1b (hereinafter referred to as a video region), an FM modulated video signal and a PCM audio signal are recorded in multiplexed form. Higher frequency components are contained in the video signal relative to the PCM signal, the frequency spectrum of the signal recorded in the video region 1b being as shown in FIG. 2. In FIG. 2, the components designated by A are the PCM signal and those designated by B are the video FM signal.
When a signal is recorded in the video region 1b, it is required to increase the rotational speed of the disk compared with the case of recording signal in the CD region 1a. Therefore, the video region 1b must be played at a higher rotational speed than the CD region 1a. As shown in FIG. 3, the rotational speed is several hundred r.p.m. for the CD region 1a, whereas the speed must be much higher for the video region, namely, about two thousand, several hundred r.p.m. at the innermost circumference of the video region 1b and about one thousand, several-hundred r.p.m. at the outermost circumference of the video region 1b.
The composite disk is, as shown in FIG. 3, provided with a lead-in area for each of the CD region and the video region, and a TOC (Table of Contents), indicative of the contents of programs for the respective regions, is recorded in each of the lead-in areas. Further, identification data is contained in the TOC of the audio lead-in area which indicates whether the disk has a video region or not.
When only the video region on a composite disk is to be played, the TOC data recorded in the lead-in area of the CD region is firstly read out to confirm that the disk includes the video region, and then the data detection point of the pickup is moved toward the lead-in area of the video region to start reading the data recorded in that area.
However, in such a playing method, a step of reading the recording data in the lead-in area of the CD region is always required, thereby causing a delay in the start of the playing of the video region.
Moreover, a so-called hi-fi video disk has recently been made available, which is a disk on which a frequency modulated video signal and a prescribed data signal are recorded in a multiplexed form. In this type of disk, a signal record as in a conventionally known video disk and a digital audio signal in a CD format are superimposed and the resultant signal is recorded.
In a reproducing apparatus for reproducing such a hi-fi video disk, a spindle servo is provided for controlling the rotation of a spindle motor which drives the disk on the basis of a phase difference between a horizontal sync signal included in the reproduced video signal and a reference sync signal so as to maintain a servo lock condition. However, since the servo lock range is narrow, typically in a range of -10% to 10% relative to the lock point (target rotational speed--see FIG. 4A), a pull-in operation has been performed during the so-called rough servo period to force the speed of the spindle motor into a lock range based on the output of a frequency generator ganged with the spindle motor.
As such, the conventional device is disadvantageous in that the cost of the device cannot be adequately reduced due to the fact that the lock range of the spindle servo is narrow and thus the frequency generator and associated components, which are generally expensive, are required. Also, the disadvantages of the hi-fi video disk also apply to the spindle servo during the reproduction of the video region of a composite disk.
As mentioned above, in a CD player, index data indicative of the program contents of the disk, i.e., the TOC, is recorded in the lead-in area of the disk. When the disk is loaded in the CD player or when the playing of the disk is ended, the pickup, which is movable in the radial direction of the disk and mounted on a slider, is moved toward the lead-in area at the innermost circumferential portion of the disk. Upon detecting the arrival of the pickup at the lead-in area by a position sensor switch, the pickup is held in the lead-in area until a new operation instruction is received. The position where the pickup is held is referred to as the rest position.
In the case of a CDV disk, a lead-in area is provided for each of the CD region and the video region. A TOC indicative of the program contents is provided for each of the respective lead-in areas. Accordingly, since the lead-in area of the CD region is determined as the rest position of the pickup, a problem arises in that, when only the video region is to be played, particularly when the video regions of a plurality of CDV disks are successively to be played, the pickup must be moved to the lead-in area of the video region from the lead-in area of the CD region, whereby a considerable time delay occurs between issuing an instruction to commence the reproduction of the video region upon depressing a PLAY key and the actual commencement of reproduction.